Enhancement of joinability and joint characteristics in mechanical joining processes by tailor heat-treated aluminium semi-finished products

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The increasing demands on the automotive industry to reduce the vehicle weight and simultaneously increase the crash safety require new design approaches. A material mix of steel and aluminum with increased strengths provides a possible solution for both problems. However, a material mix is also associated with new challenges for joining technology. In this context the use of mechanical joining processes has been intensively investigated in recent years. However, as it is known from the state of the art, the joining of high-strength materials is not yet unlimited possible. Therefore, the aim of the research project is the enhancement of joinability and the resulting bonding strength of high-strength dissimilar materials by the use of a local short-term heat treatment. The softening effect that occurs during the short-term heat treatment of aluminum alloys of the 7000 series can be used to improve the material flow of the high-strength aluminum material located on the punch side. Based on fundamental scientific investigations, the influence of tailor heat-treated blanks on the joining process and on the bonding strength of the joining point will be analyzed. This represents a new field of application for tailor heat-treated semi-finished products, which until now have only been used to expand the forming limits in part manufacturing. By analyzing the complex material flow in the shear-clinching process, a holistic process understanding will be established. Taking into account the interactions involved, an ideal strength distribution in the joining zone should be determined based on numerical models of the short-term heat treatment and the shear-clinching process. By means of experimental investigations the numerical results should be validated and the mechanical properties and the joint strength should be identified.